Method for establishing a substitute path in a network

ABSTRACT

The invention relates to a method for establishing a substitute path in a network with corresponding network nodes for path-switching between connection runs, whereby for the switching of path between two terminal nodes, a first network resource is used for the transmission and the signal transmission is interrupted in a connection run within said path. A substitute path is thus selected, in which the second resource to be selected must remain with a minimal resource loading on the switching of the network nodes. The establishment of the substitute path, corresponding to the second resource, is selected such that network nodes for the switching of retained connection runs between the original path and the substitute path must be minimally newly switched and new switching merely carried out for newly utilised connection runs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/DE2003/002697, filed Aug. 11, 2003 and claims the benefitthereof. The International Application claims the benefits of Germanapplication No. 10237584.4 filed Aug. 16, 2002, both applications areincorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The invention relates to a method for managing resources whenestablishing a substitute path in a transparently switchable network.

BACKGROUND OF THE INVENTION

From patent application DE 10105675.3 with date of publication08.08.2002 a method is known for establishing a link in an optical WDMtransmission system having a plurality of switchable optical networknodes of which at least one has a wavelength converter, whereby toestablish a link from a first optical network node via at least onesection of a link path to an Nth optical network node a first linkvector for identifying WDM transmission channels available on thesubsequent section of the link path is formed and is transmitted via theat least one WDM transmission system. By this means, a method isdescribed for establishing a path for a transparent transmission ofsignals from a source node via switchable network nodes to a terminalnode.

In the publication by G. Ahn et al., “Simulator for MPLS pathrestoration and performance evaluation”, Proceedings of “Joint 4th IEEEInternational Conference on ATM and High-speed Intelligent InternetSymposium”, 22 Apr. 2001, pages 31-36, methods for establishing asubstitute path in MPLS (=multi-protocol label switching) networks aredescribed. In particular, a “Simple-Dynamic Scheme” method is presentedin section 2 which provides a minimally short substitute path forrerouting around the fault location (e.g. an imperfection) in a network.If a fault is detected in a network node, by means of the“Simple-Dynamic Scheme” method a new substitute path to a PML(=protection merging label switching router) is switched via theshortest transmission path, no working path being utilized.

From the publication by C. Baworntummaratarat et al. “On the comparisonof optical WDM mesh network protection strategies”, ConferenceProceedings Milcom 2000, 21st Century Military CommunicationsConference, 22-25 Oct. 2000, Vol. 2 pages 886-891, a method forestablishing a substitute path in WDM networks is also known. Adistinction is drawn between “link restoration” and “path restoration”.In the case of the “link restoration” method, the interrupted datatraffic is routed around the fault location, whereas in the case of the“path restoration” method, the interrupted data traffic is routed on acompletely new path from a source node to a destination node. Althoughthe “link restoration” method is fast because it has the advantage ofremoving a fault locally and transparently, it is not suitable fornetworks with many wavelengths since the availability of free wavelengthchannels is still limited. For the “path restoration” method, threeoptions are presented in the publication. These are the “Minimal cost”method, the “Disjoint path” method and the “Single link basis” method.All the methods are what are known as pre-planned or pre-negotiatedrestoration/protection methods in which the route of the substitute pathis determined and stored even before the occurrence of a fault.

In an automatic switched transport network (ASTN) such as for example anoptical transparent network, at a location of a transmission fault e.g.as the result of the failure of a link in a switched path with a firstnetwork resource between two terminal nodes, a substitute path withrerouting around the fault location is established. For this purpose afurther network resource is needed for establishing and switching thesubstitute path. The switchover between a path and a substitute path iscarried out by means of new switchings at the terminal nodes and inaccordance with the two resources for the further switchings of theinterposed network nodes.

In order to configure the rerouting, two restoration methods areprincipally available through local or global configuration of thesubstitute path (local repair, global repair). An introduction to thesetwo methods is described in an Internet publication “Framework forMPLS-based Recoveryhttp://search.ietf.org/internet-drafts/draft-ietf-mpls-recovery-frmwrk-03.txt”,Vishal Sharma et al., July 2001.

In the case of local configuration, a shortest possible rerouting arounda fault location is established. The establishment of this rerouting isinitiated by the network node which is connected immediately upstream ofthe faulty link section. The establishment is carried out relativelyfast, but the resources for new switching do not remain optimal in termsof loading since all switchings in the original path are disconnectedand furthermore new switchings for the substitute path are establishedby means of a new resource. In the case of global configuration, thesubstitute path is recalculated as being a complete path from sourcenode X to the terminal node Y and is established through new switchingsat the interposed original network nodes still being used and at thenewly introduced network nodes. This second method enables betterutilization of the resources of the network for the substitute path, buthas the disadvantage of being slow.

SUMMARY OF THE INVENTION

The object of the invention is to specify a method for establishing asubstitute path in a network, which method enables optimum use of theresources of the network.

The object is achieved by the claims.

According to the invention, in order to configure the new resource forthe switching of link sections of a substitute path, only the changedand necessary new switchings of the newly required link sections and thelink sections used for the previous path. This has the advantage thatthe management of resources for all paths of the network is madeconsiderably easier overall because resources for the corresponding newswitching of a transparent link between two network locations from newlyestablished paths are generated not completely anew but from establishedresources of existing paths.

In a rerouting of signals e.g. due to an interruption of a link sectionor a defective network node or where a fully loaded transmissioncapacity is determined in a path, the method according to the inventionis carried out section-wise automatically.

In particular also in the switching of new link sections for thererouting of signals, a switching has to be carried out at the networknodes at which the signals are decoupled from and recoupled to theoriginal path, which switching is adapted to the new rerouting of thelink. Likewise, a minimum number of new switchings can be carried out inthe new link sections and network nodes in the rerouting if the originalconfiguration of the switching settings is known in the rerouting.

The invention is not limited to a granularity (spatial switching, groupor single wavelength switching, polarization switching, etc.) of thechannels in the network in which channels the signals are transmitted.Different multiplexing techniques can be used for transmitting thesignals. The link sections may consist of a plurality of waveguides andoptical fibers.

Advantageous further developments of the invention are specified in thedependent claims.

BRIEF DESCRIPTION OF THE DRAWING

An exemplary embodiment of the invention is explained in more detailbelow with reference to the drawing, in which

FIG. 1 shows a schematic representation of a network with aninterruption in a link section.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows schematically a network, e.g. as an optical transparentnetwork with an interruption as a fault location UL in a link sectionL4. For reasons of clarity, only link sections L1, L2, L3, L4, L5, L6and interposed network nodes N1, N2, N3, N4, N5 for a path for signaltransmission from a source node X to the terminal node Y are shown,whereby the interruption occurs in the link section L4. At the networknode N3 the interruption is identified in the link section UL and anerror message containing path and link ID transmitted via the networknodes N2, N1 to the source node X. This is made possible because thelink between the source node X and the network node N3 is stillfunctional.

In the event of there being a defect in the network node N3 itselfrather than in the link section L4, the network node N2 takes over thecommunication of the error message to the source node X. Thecommunication of the error message to the source node X always occursfrom the intact network node connected upstream of the fault locationUL.

A plurality of fault locations can also be detected whereby, where thereare e.g. two fault locations, firstly the first is updated in accordancewith the inventive method according to a second resource by the firstresource and then the third by the second resource. In other words, theresource of the path is compared with the resources of successivesubstitute paths upstream such that the resources are updated insuccession according to the invention for as long as an error message isdelivered to the source node. The fault location nearest to the sourcenode is firstly rerouted around and the other fault locations upstreamas far as the fault location nearest to the terminal node Y are thenrerouted around with the substitute paths. Switchings of identicallyused link sections between the original path and all substitute pathsare retained, i.e. not newly switched.

For the switching of link sections in the network nodes of the originalpath a first resource of the network was used for transmission.

Upon receipt of the error message at the source node X a substitute pathis chosen for rerouting around the interrupted link section L4 betweenthe source and terminal nodes X, Y according to a second resource yet tobe established. The choice of the substitute path can be carried out inaccordance with different methods known from the prior art. As anexample, two methods are based, as mentioned in a previous section ofthe description, on local or global configuration of a substitute path(“local repair” or “global repair”). In the method according to theinvention, a global configuration of a substitute path is used as arestoration method, but the original path is not yet disconnected in therestoration.

The optimum path from the source node X to the terminal node Y isdetermined by means of the routing protocol, whereby the resource of theprevious path is also utilized. In order to configure a second resourceof the network for the switching of link sections of the substitutepath, only the link sections L1 _(UL), L2 _(UL), . . . , L5 _(UL),disposed in the rerouting, with associated network nodes N1 _(UL), N2_(UL), . . . , N6 _(UL) are newly switched by means of a control signalemitted from the source node X. Here, the network nodes N1 _(UL) and N6_(UL) in the substitute path are the network nodes N2, N5 of theprevious path.

The source node X initiates the establishment of the substitute path bychecking in each individual network node of the path whether the newswitched link is identical with the switched link of the original path.Two cases occur:

-   1. Case 1 (identical): No new (physical) switching has to be carried    out, the resource of the old path has merely to be assigned to the    substitute path (path ID of the old path is replaced by the new path    ID). Here, the switchings with the components X, L1, N1, L2 and L6,    Y are retained.-   2. Case 2 (not identical): The resource reserved for the old path in    the network node under consideration—L3, N3, L4, N4, L5—is released    and the new link—N2=N1 _(UL), L1 _(UL), N2 _(UL), . . . , L5 _(UL),    N5=N6 _(UL)—is switched.

The resources are then released in the network nodes along the portionof the old path no longer needed.

1-6. (canceled)
 7. A method for managing resources when establishing asubstitute path from a source node to a terminal node in a transparentlyswitchable network for signal transmission, wherein the source node andthe terminal node are connected to a plurality of network nodes havinginterposed link sections, the method comprising: providing switchingdevices in the network nodes, in the source nodes, and in the terminalnodes for switching a plurality of paths for signal transmission betweenthe source node and the terminal node; utilizing a first networkresource controlled by the source node for the signal transmission andfor switching of the link sections within one of the paths, wherein thesignal transmission is interrupted upon occurrence of an imperfection inthe one path and an error message is transmitted from a network node tothe source node, the network node arranged upstream of the imperfectionrelative to a signal transmission direction; determining, upon receiptof the error message, by the source node a substitute path for reroutingthe signal transmission around the imperfection using a control signalgenerated by the source node; and establishing a second resource forswitching the link sections of the substitute path such that only suchlink sections disposed in the rerouting and in need of reswitching arenewly switched by the network nodes included in the rerouting, whereinthe second resource is established using the control signal and thefirst resource, and wherein switched link sections common to the pathand the substitute path are maintained.
 8. The method according to claim7, wherein the maintained switched link sections commonly assigned tothe original path and to the substitute path and the necessary switchingof link sections of the rerouting and the release of the link sectionsfrom the original path no longer used in the substitute path arecontrolled by setting up the second resource from an updating of thefirst resource at the respective network nodes.
 9. The method accordingto claim 7, wherein the link sections disposed in the rerouting areswitched with a minimum number of new switchings by the network nodes.10. The method according to claim 8, wherein the link sections disposedin the rerouting are switched with a minimum number of new switchings bythe network nodes.
 11. The method according to claim 7, wherein, whenthere is a plurality of imperfections in the path, firstly theimperfection nearest to the source node is rerouted around with a firstsubstitute path and thereafter the other imperfections in successionupstream are rerouted around with further substitute paths, wherein theresource of one of the substitute paths to be established is updatedfrom the previous established resource of the path or substitute path,and wherein switchings of identically used link sections between theoriginal path and the respective substitute paths are maintained. 12.The method according to claim 8, wherein, when there is a plurality ofimperfections in the path, firstly the imperfection nearest to thesource node is rerouted around with a first substitute path andthereafter the other imperfections in succession upstream are reroutedaround with further substitute paths, wherein the resource of one of thesubstitute paths to be established is updated from the previousestablished resource of the path or substitute path, and whereinswitchings of identically used link sections between the original pathand the respective substitute paths are maintained.
 13. The methodaccording to claim 9, wherein, when there is a plurality ofimperfections in the path, firstly the imperfection nearest to thesource node is rerouted around with a first substitute path andthereafter the other imperfections in succession upstream are reroutedaround with further substitute paths, wherein the resource of one of thesubstitute paths to be established is updated from the previousestablished resource of the path or substitute path, and whereinswitchings of identically used link sections between the original pathand the respective substitute paths are maintained.
 14. The methodaccording to claim 10, wherein, when there is a plurality ofimperfections in the path, firstly the imperfection nearest to thesource node is rerouted around with a first substitute path andthereafter the other imperfections in succession upstream are reroutedaround with further substitute paths, wherein the resource of one of thesubstitute paths to be established is updated from the previousestablished resource of the path or substitute path, and whereinswitchings of identically used link sections between the original pathand the respective substitute paths are maintained.
 15. The methodaccording to claim 7, wherein at each network node switching betweenchannels is carried out for the transmission of signals with differinggranularities.
 16. The method according to claim 8, wherein at eachnetwork node switching between channels is carried out for thetransmission of signals with differing granularities.
 17. The methodaccording to claim 9, wherein at each network node switching betweenchannels is carried out for the transmission of signals with differinggranularities.
 18. The method according to claim 10, wherein at eachnetwork node switching between channels is carried out for thetransmission of signals with differing granularities.
 19. The methodaccording to claim 11, wherein at each network node switching betweenchannels is carried out for the transmission of signals with differinggranularities.
 20. The method according to claim 12, wherein at eachnetwork node switching between channels is carried out for thetransmission of signals with differing granularities.
 21. The methodaccording to claim 13, wherein at each network node switching betweenchannels is carried out for the transmission of signals with differinggranularities.
 22. The method according to claim 14, wherein at eachnetwork node switching between channels is carried out for thetransmission of signals with differing granularities.